This invention relates to an apparatus and method for heating fluid in a subterranean formation, which has poor flowabilty due to the buildup of paraffin, or asphaltene on the walls of the production tubing or in the well bore. More particularly, the present invention relates to an apparatus and method of improving flowabilty of subterranean formation fluid by using an inline heating method.
One of the problems associated with oil production is the deposition of paraffin or asphaltene on the walls of production tubing or the well bore. The oil is pumped to the surface or forced to the surface from a relatively hot area through a cool zone where the temperature of formation is less that the solidification temperature of paraffin. Once paraffin or asphaltene separate from the crude oil fluid flow, they tend to adhere to the production line walls causing a restriction in the tubing. Over time the paraffin builds up on the walls of the production tubing and significantly affects the production flow. As the crude oil is pumped to the surface, the gas from the reservoir also rises to the surface. Reservoir gas tends to decrease the reservoir pressure and increase the time the crude oil is flowing through the production tubing. As a consequence, the reduced flow of oil loses speed and pressure as it travels from downhole to the surface. The decreased temperature increases the viscosity of the oil and further reduces the flow rate.
Such phenomenon is well known in the field and various methods have been employed to solve the problem. One such method is the so-called “Hot Oil Treatment.” According to the hot oil treatment method steam is pumped under significant pressure in the area between the casing and the tubing. The pressure applied during this process forces paraffin residue into the production formation. This method is ineffective as interaction of steam pressure in the producing zone frequently results in clogged perforations and ultimately the decline or loss of production. The pressure steam method is also time consuming, and requires down time to complete, is expensive and presents significant risks to the operator.
Another method that is conventionally used in the oil industry to treat paraffin deposits requires stopping on the production, retrieval of the tubing, cleaning by scraping or steam, the inner wall of the well string to remove the paraffin and asphaltene deposits and then replacing the tubing back into the well. This method is also time consuming and costly and does not prevent future paraffin deposits in the pipes. The method is merely a maintenance procedure that works for a short period of time. Additionally, the risk of loss of production while the well is shut-in, coupled with the maintenance expense, makes many wells unprofitable to produce if such method is used.
Still another commonly employed method is a chemical treatment using solvents that are introduced in the well bore in an effort to dissolve the paraffin deposits and improve the flow of crude oil.
All these methods and systems have minimal success in addressing the problem as it occurs. Additionally, the conventional solutions do not take into consideration the flash ignition prevention in the design. The conventional tools are single units with limited heating capabilities that cannot be extended or added to, to cover a greater zone of treatment. Furthermore, the electrical heating devices used in conventional downhole heaters tend to allow leakage at electrical connections or at wire feed-through areas, which caused serious problems in the volatile environment downhole.
One of the more serious problems is the failure of the conventional tools to detect and monitor downhole temperatures at the vicinity of the heater and thereby regulate the temperature in the critical areas. Another serious problem associated with conventional tools is failure to allow dumping of the fluid while at the bottom of the downhole fluid and crude oil while the heater is introduced in the flow path as part of the well string. Additionally, solid wall liners used in the heating devices do not prevent gas lock whereby gasses are prevented from escaping from the well bore tubing, which significantly impairs the production pressure.
The present invention contemplates elimination of drawbacks associated with conventional systems and provision of an inline downhole heater that can be controlled and regulated from the surface as it heats the oil passing through the production tubing.